Multistage cascade amplifier



Oct. 28, 1952 cHARcHlAN 2,615,998

MULTISTAGE CASCADE AMPLIFIER Filed Jan. 31, 1948 Patented Oct. 28, 1952 UNITED .S TATES 'iE'i" OFFICE MULTISTAGE CASCADE AMPLIFIER ware Application January 31, 1948, SerialNo. 5,600

.7 Claims.

This invention relates to microwave tube coupling systems and more especially to improvements in the coupling of microwave tubes as part of a coaxial transmission line system.

In coupling microwave tubes to coaxial lines or in coupling such tubes to each other, it has heretofore been necessary to provide complicated piping arrangements with mechanism for tuning input and output connections.

A principal object of the invention is to provide a simplified arrangement for couplin a plate or output electrode of one electron tube to the cathode or input electrode of another electron tube, employing a tuned coaxial line section which is terminated at opposite ends respectively by said plate and cathode.

Another object is to provide an improved arrangement for coupling microwave tubes in cascade and as integral parts of a coaxial transmission line system, wherein the number of piping connection units is reduced while at the same time reducing the number of tuning adjustments for the cascaded tubes.

A feature of the invention relates to a coaxial line system wherein a plurality of grid-controlled microwave tubes are interposed between sections of the coaxial line, the center conductor of one line section forming a single direct couplin between the anode or plate of one tube and the cathode of a succeeding tube.

Another feature relates to a coaxial line transmission unit employing a pair of cathode driven ultra high-frequency electron tubes with the plate or anode of one tube terminating the end of ithecenter conductor of one section of said line and the cathodeof the succeeding tube terminating the opposite end of said line section, in conjunction with means to tune said section to an even number of quarter-wavelengths.

A further feature relates to an oscillator-amplifier combination employing a pair of ultrahigh-frequency grid-controlled electron tubes which are serially interposed between successive sections of a coaxial transmission line so that the anode of the oscillator and the cathode of the amplifier form a single structural unit with an intervening section of the central conductor of said line.

A still further feature relates to an ultra-highfrequency coupling arrangement between successive electron tubes, wherein the high output impedance of the first tube is coupled to the relatively low input inpedance o the succeedin tube by an effective single coaxial line section. This eliminates the usual separate tuning input and output circuits between the tubes since the coupling can be effected by tuning the said line section to an even multiple of a quarter-wavelength.

The above-mentioned andother features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood, by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawing.

In the drawing which shows, by way of example, a two-stage amplifier system, the numeral 1 represents any well-known form of grid-controlled electron tube such as is conventionally used in ultra-high-frequency or microwave systems, of which the so-called lighthouse tube is typical. It will be understood of course that the invention is not limited to any particular construction of tube so long as the various electrodes are designed for ultra-high-frequency operation and can be conveniently connected into a coaxial transmission line system. Thus, if desired, these tubes may be of the construction illustrated in U. S. Patent 2,391,927, or U. S. Patent #2,11,523, with planar cathode, planar grid, and planar anode. The tube 1 may com-prise an evacuated glass envelope 2 having an electron-emitting cathode 3 for example in the form of a metal thimble which is vacuum-tight sealed through the glass wall of the envelope and is arranged to be coupled to the pipe 4. The cathode 3 is provided internally of the envelope with a suitable filament or heater wire, one end of which is connected to the cathode 3 and the other end of which is connected to a rod or wire 5 passing centrally through pipe 4, but D. C. insulated therefrom. The current for heating the filament is connected externally across pipe 4 and wire '5.

The control grid 6 of the tube l is provided with the usual disc seal 7 through th envelope, to which is connected the grid bell 8 in the form of an open-ended metal cup. Fitted in telescopic adjustable relation over the end of bell 8 is a metal tuning sleeve 9. Cooperating with pipe 4 to form therewith a coaxial transmission line section is a hollow outer conductor 1 E), which is joined at one end by the perforated disc H to pipe 4. Conductor ID has an opening :2 on one side communicating with the outer conductor l3 of a coaxial signal input line, the center conductor M of which is connected to pipe 4, so that the signal waves impressed on the input line l3hl correspondingly drive the cathode 3. The plate or anode I5 of tube I may be in the shape 3 of an inverted metal thimble vacuum-tight sealed through the tube envelope and connected to a metal pip l6 through an intervening insulating ring or bushing ll. The opposite end of pipe I6 is united to the cathode I6 of a second microwave amplifier tube H), which may be similar in construction to the tube the cathode l8 being provided with a heater filament 20, one end of which is connected to the cathode and the other end of which is connected to a metal rod or wire 2| which is centrally located within the pipe l6 but D. C. insulated therefrom. The current for heating the cathode i8 is connected externally by conductors 22, 23, to a suitable current source.

The disc seal 24 for the control grid 25 is connected to a grid bell 26 which in turn is provided with a telescopically adjustable tuning sleeve 21. Surrounding the pipe I6 is a hollow metal conductor 28 which forms with the pipe IS a coaxial transmission line section and the conductor 28 may be provided with a telescopically adjustable sleeve 29 for adjusting the effective electrical length of the coaxial line sections l628. It will be observed that the elements l6 and 28 are of the same diameters as the corresponding elements 4 and Ill. The plate or anode 30 of tube I9 may be in the form of an inverted thimble vacuumtight sealed through the wall of the tube and connected to a metal pipe 3| through an intervening insulator sleeve or bushing 32. The D. C. plate potential for plate 30 is supplied by a conductor 33 passing centrally through the pipe 3| but D. C. insulated from the said pipe. The amplified signal output is taken off by a conductor 34 which is connected to the pipe 3|. The D. C. plate potential for the anode of tube is supplied by a conductor 35.

The foregoing assembly is housed within a tubular metallic shell 36 and an adjustable annular piston-like metal member 3! is fitted into the upper end of shell 36 to tune the cathode circuit of tube Likewise, an adjustable annular metal piston-like member 38 is fitted within the opposite end of the shell to tune the anode circuit of tube 26. Shell 36 has a side arm 39 which is arranged to be connected to a coaxial cable 40, the center conductor 4| of which connects to the grid 6 to supply the necessary D. C. grid bias therefor. Likewise, a hollow metal conductor 42 extends between an opening in the shell 36 and a corresponding opening in pipe IE, to provide a shielded passage for the supply conductors 22, 23 and 35, above mentioned. An additional tubular side arm 43 is provided in the shell 36 through which the output conductor 34 passes. An adjustable metal piston-like member 44 is also slidably mounted within the side arm of tube 43. The shell 36 may be provided with suitable apertures 45 for permitting telescopic adjustment of the tuning sleeve 28, and with similar apertures 46 for adjustably tuning the sleeve 9. Likewise, the sleeve 29 may be provided with an adjusting member 41 accessible externally of the shell 36, and another annular tuning piston 48 may be provided between the member 28 and the shell 36 and which can be adjusted by an external tuning arm 49.

From the foregoing, it will be seen that both the tubes and I9 are cathode driven, the plate l5 of tube I being coupled to the cathode |8 of tube H! by a coaxial line consisting of the conductors l6 and 28. In accordance with one phase of the invention, this line is tuned to an even multiple of a quarter-wavelength of the operating frequency of the system so as to match the 4 high impedance plate output of tube to the low impedance cathode input of tube I9, and eliminating the usual separate tuned plate and tuned input circuits ordinarily required for cascade coupled tubes.

Another advantage of the foregoing described construction is the avoidance of asymmetry which would ordinarily occur when side input feed and side output are taken oif from a coaxial transmission line system. It further provides a simplified coupling arrangement between microwave triodes which are coupled by a coaxial line and so that the elements 8 and 36 and elements 26 and 36 form in effect tunable cavities. It permits the building of an oscillator-amplifier unit operating at microwave frequencies without the necessity of employing grounded grids and without the necessity of employing separately tuned cathode and tuned plate circuits. While in the foregoing it has been mentioned that the tubes and |9 are amplifier tubes, it will be understood that the tube I may be an oscillator or a frequency multiplier. The cathode line of the oscillator tube is tuned by the adjustable piston or plunger 31. The plate circuit of amplifier I9 is likewise tuned by the piston or plunger 38. The grid circuit of oscillator is tuned by the sleeve 9 and the grid of amplifier tube I9 is tuned by the sleeve 27.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention.

What is claimed is:

1. An electron tube system for operation at ultra-high-frequency, comprising a pair of gridcontrolled electron tubes to be connected in cascade, a coaxial wave transmission line section coupling the output of one tube to the input of the other tube, said section having one of the conductors thereof terminated at one end in the anode of one tube and terminated at the other end in the cathode of the other tube, said line section being dimensioned to an even multiple of a quarter-wavelength at the operating frequency of the system whereby both the output circuit of said one tube and the input circuit of said other tube are tuned.

2. An electron tube system for operation at ultra-high-frequency, comprising a first gridcontrolled electron tube, a second grid-controlled electron tube, a coaxial wave transmission line comprising an input section, an output section, and an intervening inter-tube coupling section, said coupling section being terminated at its input end by the anode of the first tube, at its opposite end by the cathode of the second tube, and being tuned to an even multiple of a quarterwavelength at the operating frequency of the system whereby both the output circuit of said first tube and the input circuit of said second tube are tuned.

3. An electron tube system according to claim 2 in which said intervening coaxial line section has a central hollow conductor formed in two parts which are D. C. insulated from each other. and supply conductors respectively for the anode of the first tube and for the cathode of the second tube passed interiorly through said hollow conductor.

4. An electron tube system for operation at ultra-high-frequency, comprising a first gridcontrolled electron tube, a second grid-controlled electron tube, coaxial line means couplin the cathode of the first tube to a signal source for excitation thereby, other coaxial line means coupling the plate of the first tube to the cathode of the second tube for exciting the cathode of the second tube by the signals at the plate of the first tube, said other coaxial line means comprising a central conductor forming an integral unit with the anode of the first tube and with the cathode of the second tube, an outer tubular transmission line conductor for said central conductor, and means to tune said other coaxial line means to an even multiple of one quarter-wavelength at the operating frequency of the system whereby both the output circuit of said first tube and the input circuit of said second tube are tuned.

5. An electron tube system according to claim 4 in which one end of said other coaxial line section is connected to the anode of the first tube and the opposite end of said other coaxial line section is connected to the cathode of the second tube.

6. An electron tube system according to claim 5 in which each of said tubes is of the type having a circular cathode, a circular grid, and a circular anode, the anode of the first tube having a cylindrical flange integrally united to said central conductor of said other coaxial line means, and the cathode of the second tube having a cylindrical flange integrally united to the opposite end of said other coaxial line means.

'7. An electron tube system for operation at ultra-high-frequency, comprising a first electron discharge tube having cathode, control grid, and anode, a second electron discharge tube having cathode, control grid, and anode, a, coaxial line comprising an input section, an intertube coupling section, and an output section, means connecting said line sections and said tubes together as an integral unit with the anode of the first tube directly connected to the cathode of the second tube for signal excitation of said cathode by means of said coupling section, said coupling section having an electrical length which is an even multiple of a quarter-wavelength at the operating frequency of the system, a tunable grid bell connected to the grid of the first tube, a tunable grid bell connected to the grid of the second tube, a conductive shell surrounding the said line sections and the said tubes, tuning pistons located between said shell and the input end of the input line section, tuning pistons located between said shell and the output line section, and separate means to tune both of said grid bells.

BENJAMIN MALCOLM CHARCHIAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,088,722 Potter Aug. 3, 1937 2,143,671 Zottu Jan. 10, 1939 2,419,985 Brown May 6, 1947 2,423,548 Bels July 8, 1947 2,426,185 Doherty Aug. 26, 1947 2,434,115 McArthur Jan. 6, 1948 2,465,801 Gurewitsch Mar. 29, 1949 

